The list of bugs solved in 4.0.1 includes (the complete description of each issue can be checked here):

Context:

• 1793 Virtual router should also include a router advertisement daemon (radvd)

OpenNebula Core:

• 2009 Admin can recover VMs by trigger actions or transitions

Virtualization Drivers:

• 1995 DATA_VMX not working when no OS disk
• 2025 EC2 drivers do not get all the information

Sunstone:

• 2057 Template DISK size always in MB
• 2037 Check if session cookie has been changed
• 2000 Include MD5 check attributes in Image Template
• 1938 VM wizard disk tab is missing some attributes
• 1976 When a quota is edited, sunstone fills empty inputs with 0 as the default value instead of -1
• 1979 Selected IDs are not detected when the table page is visible. This breaks actions and auto-refresh disable condition
• 2003 Error if Volume Group Name is specified when creating a new ISCSi datastore
• 2012 Default value for logo in sunstone-views.yaml doesn't honor reverse proxies
• 2013 VNC secure websockets does not work
• 2034 improve cookie expiration time handling

The migration from OpenNebula 4.0 is straightforward by just upgrading the database version using the procedure described here.

If you are upgrading from OpenNebula 3.8 or any other previous version please refer to the information included in the OpenNebula 4.0 release notes.

We'd like to thank the great feedback received, it is an essential part of the process that makes OpenNebula a reality, and the primary source of improvement. A detailed list of people that have contributed to OpenNebula 4.0, can be found in the Eagle release notes

More information about the project can be found at the project web page. You may be also interested in checking the OpenNebula Ecosystem that includes many interesting projects contributed by the community to enhance or add new features to OpenNebula.